1. Field of the Invention
This invention relates to marine propulsion devices such as outboard motors, stern drive units and the like, and more particularly relates to improving safety and hydro-flow thrust from hydro-drive devices.
2. Description of the Related Art
For over 100 years screwdriven propellers and impellers have been used to propel marine vehicles. Over the years, the technology of the propulsion drives has changed incredibly. However, the technology of the propeller/impeller, aside from sizes and shapes, has remained relatively unchanged.
As a propeller/impeller turns, water is drawn in and is accelerated through the flywheel action of a propeller/impeller increasing the higher-velocity stream of water behind (aft) the propeller/impeller. Accelerating the water by the action of pulling water in and pushing water out at a higher velocity is commonly known as adding momentum to the water. This change in momentum or acceleration of the water (hydro-flow) results in a force called “thrust.” A curvature of the propeller/impeller blade creates low-pressure on the back of the blade, thus inducing lift, much like the wing on an airplane. With a marine propeller/impeller, the lift is translated into horizontal movement.
The spinning blades of the propeller/impeller produce hydro-flow thrust, which can depend upon many factors. Examples of such factors include volume of water accelerated per time unit, propeller/impeller diameter, velocity of incoming hydro-flow, density of water, and the SHP (shaft horsepower) accelerating the propeller/impeller. As in any motorized industry, great expense and effort is put into the improvement of efficiency and power of the motor. Perhaps the largest factor relating to efficiency and power or hydro-flow thrust is the propeller/impeller.
The propeller shroud also has the additional benefit of protecting submerged objects from contact with the propeller/impeller. With ever increasing marine vehicle ownership, incidents of injury or damage due to propeller/impellers strikes, though unfortunate, seem commonplace. The shroud prevents swimmers, water skiers, water sports enthusiast, and marine life from encountering or being entangled by the spinning blades of a propeller/impeller. Safety is accomplished by enclosing the entire flywheel area of the propeller/impeller within the propeller shroud.
Shrouds are available that may perform the function of protecting people, marine sea and plant life from the propeller/impeller. However, available shrouds tend to restrict water flow, increase drag, or modify the exiting water stream. Each of the aforementioned actions appreciably reduces hydro-flow thrust, thus negatively affecting the performance.
From the foregoing discussion, it should be apparent that a need exists for a system and apparatus that protects people, marine and plant life, and increases hydro-flow thrust generated from a boat propeller/impeller. Beneficially, such a system and apparatus would increase hydro-flow, decrease drag, and improve performance by increasing the volume and velocity of hydro-flow thrust in a vortex exiting the shroud